It is known that for recycling containers for foodstuffs, and in particular PET bottles for beverages, the labels made of paper or of plastics first have to be removed, for example glued tubular labels made of heat-shrinkable plastics that are often associated with the aforesaid containers.
For example, from U.S. Pat. No. 4,209,344 and WO 9208591 plants are known in which paper labels in general are removed by a process of washing in a bath of hot water with great agitation with the addition of a suitable cleaning chemical; plants of this type, in addition to be extremely bulky, require large water consumption and thermal energy consumption.
On the other hand, particular problems exist for removing tubular labels made of plastics, for example PVC heat-shrinkable labels from containers and/or PET bottles, inasmuch as removal thereof is extremely difficult with conventional plants; in fact the containers could break if subjected to great stress, with the consequent loss of plastics having a high financial value.
As the use of PET containers with tubular labels made of plastics has become increasingly widespread over the years in the food industry and in view of the high value of PET material, collecting Post-consumer containers and/or bottles intended to be recycled has taken on significant economic importance.
During the collection of Post-consumer material, the PET bottles are normally compressed into bales and are greatly deformed together with solid bodies and other foreign matter, which has to be eliminated by a suitable pre-washing step; after pre-washing the bottles are ground and subjected to other treatments before being transformed into pellets for further use.
As the plastics of the labels are a major pollutant in the process of recycling PET various technologies have been developed for trying to eliminate all or most of the labels from the PET bottles before transformation into granules.
For example, in U.S. Pat. No. 4,379,525 a method has been proposed in which the containers with the labels are ground finely by stirring the ground granules in a bath of hot water to remove the label part that remained adhering thereto; subsequently, filtering and recirculating steps of the ground granules and of the process water occur until the material of the labels has been completely eliminated. A similar method, in addition to requiring an equally complex system, entails great energy expenditure and consequent high financial costs.
In DE 10308500 a method has been proposed for dry removal of the labels from the containers, before grinding, according to which the containers with the labels are passed through an apparatus comprising a stator with holes, having a polygonal section, inside which a rotor rotates that comprises a plurality of large cross-shaped tools, which are suitable for generating axial and tangential forces on the containers inside the stator.
Although the rotor is rotated at a relatively low number of revolutions, comprised between 500 and 2500 revolutions per minute, the proposed solution is difficult to adapt to removing labels from containers that during collection and storage have been greatly deformed, crushing the labels axially or sideways; further, with high tangential speeds of the tools of the rotor it is not excluded that part of the containers can be partially broken with the detachment of the necks of the bottles and consequent loss of plastics of high financial value.
In turn, WO 2011012113 proposes an apparatus for removing labels from PET containers or bottles, comprising a cylindrical stator, inside which a polygonal rotor rotates that is provided with a plurality of axially spaced tools; the tools are configured with a step profile and are angularly oriented for dragging in rotation the containers and for generating mechanical stress that is suitable for removing the labels and possible foreign bodies that have remained adhering to the containers. Also this solution is not without drawbacks because of the great mechanical stress and the forces of the impact generated by the tools during rotation of the rotor, with consequent breakage of the containers and loss of plastics. In particular, owing to the step profiles of the tools, between the stator and the rotor a gap is defined the thickness of which is not uniform, but varies from zone to zone according to the pattern of the profile of the various tools. In other words, the bottles advance in the gap, traversing narrower passage zones at the more protruding parts of the tools, and wider passage zones, at the less protruding parts of the tools. Such a configuration can generate a “wedging” and/or blocking effect for the bottles that often leads the latter to undergo significant mechanical stress until consequent breakage.